Introduction of a femto cell base station (Home NodeB, or HNB) is being promoted in a mobile communications system such as of 3G (3rd Generation) and LTE (Long Term Evolution). A femto cell base station is a base station device which builds a femto cell having a communication range within some tens of meters in radius. A femto cell base station assumes the role of supplementing an area which cannot be covered by the wireless area of a macro base station having a communication range of a several kilometers in radius, and of offering a high-quality communication service in a home and the like. Meanwhile, in LTE, a femto cell base station is called HeNodeB (Home eNodeB) or HeNB.
In terms of a system configuration, each femto cell base station is given accommodation by a femto gateway that is an upper device. Its specification is disclosed in non-patent document 1. Meanwhile, a gateway may be abbreviated to GW hereinafter. A femto GW is connected to MME (Mobility Management Entity) and S-GW (Serving Gateway) that are higher rank core nodes. Furthermore, a femto GW can be connected to a plurality of higher rank core nodes for the purpose of load sharing and the like of the higher rank core nodes.
Here, it is assumed that a failure has occurred in a femto GW and communication with all higher rank core nodes has become impossible. In this case, in a wireless area formed by each femto cell base station connecting to the femto GW, a communication service cannot be provided for a terminal any more. However, each femto cell base station tries to continue communication with the femto GW. For this reason, in a terminal connecting with each femto cell base station, a state not to be able to enjoy a service will continue.
A method to settle this problem is disclosed in patent document 1, for example. In this technology, when a failure occurs in the connection between a femto GW and a higher rank communication network, the femto GW transmits a domain regulation message to each accommodated femto cell base station, first. Then, a femto cell base station transmits a message to the effect that access is not possible to a connected terminal. When this message is received, the terminal cuts a connection with the femto cell base station. Then, by user's operation, the terminal for which connection has been cut tries reconnection by the following two methods. 1) A femto cell base station that can communicate is searched for from adjacent femto cell base stations successively. 2) A macro base station which can be connected is searched for.
In this way, according to the technology of patent document 1, even if a connected femto GW becomes unable to communicate with a higher rank core node, communication with a core network can be recovered without repeating wasteful retries.